1. Field of the invention
The present invention concerns an ultra-high-speed extracorporeal ultrasound hyperthermia method and treatment device.
2. Description of the prior art
It is known, in particular from RE 33,590, to use a focussed ultrasound beam to cause extremely localized heating of biological tissue in order to destroy tumors. The beam is transmitted in the form of periodic wave trains having a predetermined frequency peak power and duration.
In the device described in the patent referred to above, the beam high frequency ranges between 0.5 and 5 MHz, for example, the lower frequencies being used to destroy the deeper structures within the body and the electric peak power which excites the transducer is comparatively low (10 to 100 watts, the higher powers being used to destroy the deeper structures).
These wave trains, the duration of each of which is about 1 second, are separated by intervals of about 1/10 second during which it is possible to carry out real time (usually type B) ultrasound scanning to relocate the focus relative to the target (which is affected by natural movements of the tissues caused by breathing) or to examine the damage sustained by the tissues in the treated area.
With the power level and frequencies employed--which depend on the depth of the target area--the target temperature is increased to approximately 45.degree. C., a temperature which is sufficiently high in principle to destroy malignant cells. It has been thought previously that an excessive increase in the temperature of the target area could cause serious burns in the surrounding area as the result of thermal diffusion.
As a result, treatment times are relatively long, possibly several tens of minutes or even several hours.
The invention is based on the discovery that increasing the peak power of the waves used by a factor of 10 to 200 or more, depending on the depth and the absorbing power of the target area, makes it possible, by causing an ultra-high-speed temperature rise, to significantly reduce the effects of thermal diffusion and to destroy the target area in time periods in the order of one second or less.